The present invention relates to an improved adhesive composition. More particularly, it relates to a two component type adhesive composition of which the main component of the composition enhances storage stability.
There are known a variety of reactive type adhesive compositions which do not substantially contain any solvent and are cured by the polymerization of the monomeric component therein to achieve a firm adhesion of the various materials. One example is a two component type adhesive composition which essentially consists of a main or first component comprising a polymerizable monomer, such as an acrylic or methacrylic monomer, and a free radical producing agent, such as an organic peroxide, and an activating or second component composition comprising an activator which initiates the polymerization of the polymerizable monomer at room temperature. As the activator, there is preferably employed one which can assure the production of sufficient adhesion strength to the polymerized monomer even when used in a small amount.
An adhesive composition is generally required to exhibit an excellent performance in adhesion rate and adhesion strength. It is simultaneously important that these properties are maintained over a long period of time. Quite often, the main component in a two component type adhesive composition produces gelation or deterioration of performance within a relatively short period of time.
U.S. Pat. No. 3,890,407 discloses a two component type adhesive composition of which the main component comprises a solution of chlorosulfonated polyethylene or a mixture of chlorinated polyethylene with a sulfonyl chloride, in an acrylic or methacrylic monomer and an organic peroxide. This adhesive composition is excellent in adhesion strength but insufficient in storage stability.
U.S. Pat. No. 3,962,372 proposes the improvement of the storage stability of the adhesive composition disclosed in U.S. Pat. No. 3,890,407. Namely, it proposes the incorporation of 2,6-di-t-butyl-4-methylphenol (BHT) as a stabilizer with the main component in an amount of 1 to 4 parts by weight to 1 part by weight of a hydroperoxide as the radical producing agent therein. It could be experimentally confirmed that the above proposal improves the stability. However, it was simultaneously ascertained that in the test of accelerated storage stability, gelation takes place at 50.degree. C. within 7 to 10 days. For practical use, such gelation should not take place for at least 20 to 30 days. Thus, the improved adhesive composition proposed is still not satisfactory in this respect.